Popular old record though initially unsuitable (5)
I believe the answer is:
inept
'unsuitable' is the definition.
(I've seen this before)
'popular old record though initially' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'old record' becomes 'EP' (abbreviation for extended play record).
'initially' indicates taking the first letters.
The first letter of 'though' is 't'.
'in'+'ep'+'t'='INEPT'
(Other definitions for inept that I've seen before include "Lacking any competence" , "Lacking skill" , "pointless" , "Clumsy, bumbling" , "Useless, awkward" .)